U.S. patent number 5,635,721 [Application Number 08/528,965] was granted by the patent office on 1997-06-03 for apparatus for the liner acceleration of electrons, particularly for intraoperative radiation therapy.
This patent grant is currently assigned to Hitesys S.p.A.. Invention is credited to Gianluca Bardi, Mario Fantini, Sandro Sandri, Felice Santoni.
United States Patent |
5,635,721 |
Bardi , et al. |
June 3, 1997 |
**Please see images for:
( Certificate of Correction ) ** |
Apparatus for the liner acceleration of electrons, particularly for
intraoperative radiation therapy
Abstract
An apparatus for the linear acceleration of electrons,
particularly for intraoperative radiation therapy, including: an
articulated structure for moving a radiating head that comprises an
acceleration structure constituted by a plurality of cavities; a
modulator for generating, controlling, and transmitting a
radio-frequency to the cavities of the acceleration structure; and
processing and control devices adapted to control the apparatus;
the modulator is separate from the radiating head and the
connection occurs by virtue of waveguide means adapted to carry the
radio-frequency to the acceleration structure.
Inventors: |
Bardi; Gianluca (Florence,
IT), Fantini; Mario (Rome, IT), Sandri;
Sandro (Rome, IT), Santoni; Felice (Grotte Santo
Stefano, IT) |
Assignee: |
Hitesys S.p.A. (Aprilia,
IT)
|
Family
ID: |
11356051 |
Appl.
No.: |
08/528,965 |
Filed: |
September 15, 1995 |
Foreign Application Priority Data
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|
|
|
|
Sep 19, 1994 [IT] |
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LT94A0012 |
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Current U.S.
Class: |
250/492.3;
315/5.41; 315/5.42; 378/64; 378/65; 600/1; 600/2 |
Current CPC
Class: |
A61N
5/01 (20130101); A61N 5/10 (20130101); H05H
7/22 (20130101); A61N 2005/1089 (20130101) |
Current International
Class: |
A61N
5/01 (20060101); A61N 5/10 (20060101); H05H
7/22 (20060101); H05H 7/00 (20060101); H01J
033/00 (); H05H 009/00 () |
Field of
Search: |
;250/492.3 ;600/1,2
;378/64,65 ;315/5.41,5.42 |
References Cited
[Referenced By]
U.S. Patent Documents
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|
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3796906 |
March 1974 |
Henry-Bezy et al. |
5321271 |
June 1994 |
Schonberg et al. |
|
Primary Examiner: Berman; Jack I.
Attorney, Agent or Firm: Modiano; Guido Josif; Albert
Claims
What is claimed is:
1. An apparatus for the linear acceleration of electrons,
comprising:
an articulated structure for moving irradiation means that comprise
an acceleration structure constituted by a plurality of
cavities;
modulation means for generating, controlling, and transmitting a
radio-frequency to said cavities of said acceleration structure;
and
processing and control means adapted to control said apparatus,
said modulation means being separate from said irradiation means,
the connection occurring by virtue of waveguide means adapted to
carry the radio-frequency to said acceleration structure.
2. An apparatus according to claim 1, wherein said waveguide means
comprise a flexible waveguide adapted to connect said modulation
means to said irradiation means.
3. An apparatus according to claim 1, wherein said articulated
structure comprises a robot for the movement of said irradiation
means, said robot being arranged on a supporting structure fixed to
the ground.
4. An apparatus according to claim 3, wherein said robot comprises
four articulated segments that are movable with respect to each
other and allow said irradiation means to move with six degrees of
freedom.
5. An apparatus according to claim 1, wherein it comprises
processing means adapted to manage said apparatus, said processing
means being connected to said modulation means.
6. An apparatus according to claim 1, wherein said plurality of
cavities of said acceleration structure are interconnected by means
of vacuum-tight braze welds, the cavities from the first to the
fifth one having increasing lengths, the subsequent cavities being
identical in length, said plurality of cavities producing a
self-focusing of the electron beam.
7. An apparatus according to claim 6, wherein said acceleration
structure comprises a cathode located in front of said first cavity
and a titanium lamina located outside the last cavity.
8. An apparatus according to claim 1, wherein said modulation means
comprise a magnetron, a radio-frequency modulator, and a cathode
modulator adapted to enable said cathode.
9. An apparatus according to claim 6, wherein said acceleration
structure comprises a titanium lamina located outside the last
cavity.
10. An apparatus according to claim 1, wherein said modulation
means comprise a magnetron and a radio-frequency modulator.
11. A process for performing intraoperative radiation therapy by
using the apparatus for the acceleration of electrons defined in
claim 1, comprising the steps that consist of an instruction step,
a learning step, a verification step, and a therapy step.
12. A process according to claim 11, wherein said instruction step
consists in making said apparatus follow manually the perimeters of
the areas to be treated; wherein said learning step consists in
storing said perimeters on the part of said apparatus; wherein said
verification step consists in verifying said paths and in
simultaneously entering the parameters that indicate, for each
path, doses and energy of the electron beam used for the treatment;
and wherein said therapy step consists in performing the
irradiation of said defined areas according to said set doses and
energy.
Description
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for the linear
acceleration of electrons, particularly for intraoperative
radiation therapy.
Intraoperative radiation therapy is a therapeutic method used in
treating deep neoplasms and consists in delivering a single intense
dose of radiation onto a tumoral mass, preventing the dose from
affecting the surrounding healthy tissues.
Its field of utilization ranges from surgically inoperable tumors,
to tumoral residues after partial surgical exeresis, to a tumoral
bed after full surgical removal. In this manner, by delivering the
dose of radiation directly onto the tumor or onto the macroscopic
or microscopic tumoral residue, it is possible to spare the
peritumoral healthy tissues that are instead affected by radiation
in conventional radiation therapy with external beams.
Currently there is growing interest in the use of this therapeutic
method for a wide range of tumors, particularly those affecting the
abdomen, the pelvis, and the chest. The association of this therapy
with surgery and with conventional radiation therapy allows to
considerably improve local control of advanced-phase neoplasms.
Large electron accelerators, which allow to treat a patient both
with an electron beam and with X rays, have been successful in the
execution of this intraoperative radiation therapy. Use of
electron-bee therapy offers high versatility in treating tumoral
residues after surgical removal as well as tumoral masses deemed
inoperable.
However, large electron accelerators have some drawbacks which can
limit their use.
A first drawback can be found in their high cost.
A second drawback is the considerable bulk of the apparatus.
The real drawback of electron accelerators, however, resides in the
intense irradiation produced, which cannot be confined with simple
movable panels, and therefore in the consequent need for heavily
shielded work sites.
Special radiation-therapy bunkers are therefore built for this
purpose with concrete walls one or two meters thick. The shielding
of radiation-therapy sites is governed by specific safety
regulations.
For intraoperative radiation therapy, the patients are transferred
under anaesthesia from the operating room to the radiation-therapy
bunker, under constant monitoring; the subsequent steps of the
process and, usually, the final step of the surgery being performed
on the patient take place in said bunker. Only in rare cases the
operating rooms are located directly in a bunker so as to
simultaneously act as a radiation-therapy room as well.
The need to transfer the patient to a location other than the
operating room causes problems linked to the risks of transferring
the patient under anaesthesia and to the time that elapses between
surgical exeresis and subsequent radiation therapy.
It is furthermore necessary to strictly schedule each operation
according to the availability of access to the radiation-therapy
site, and this increases the working time requirements and reduces
the number of patients who can utilize this radiation therapy.
Furthermore, in current electron accelerators the irradiation unit
(known as "radiating head"), the modulator, and the components for
therapy are assembled in a single block that is difficult to move
due to its weight and size.
This does not allow the radiating head to be placed precisely in
space and to be moved in a flexible manner, so that the electron
beam treats the entire tumoral mass involved, despite the irregular
shape that said mass may have.
In order to avoid this drawback, with the linear electron
accelerators used so far it is necessary to increase the
cross-section of the radiation beam, with greater problems in terms
of shielding and damage to healthy surrounding tissues.
Finally, the difficulty in moving the radiating head makes it
impossible to vary the dose of emitted radiation for each point of
the tumoral mass, so as to administer the dose prescribed by the
physician to each area.
SUMMARY OF THE INVENTION
A principal aim of the present invention is therefore to provide an
apparatus for the linear acceleration of electrons, particularly
for intraoperative radiation therapy, which can be used directly in
the operating room without special radiation-protective
measures.
Within the scope of this aim, an object of the present invention is
to provide an apparatus for the linear acceleration of electrons
that allows the flexible and precise movement in space of the
electron beam to treat tumoral masses having variable and different
shapes.
Another object of the present invention is to provide an apparatus
for the linear acceleration of electrons that allows to provide the
electron acceleration section separately from the radio-frequency
generation and control section.
A further object of the present invention is to provide an
apparatus for the linear acceleration of electrons that allows to
achieve a very low X-ray level that can be easily shielded.
Another object of the present invention is to provide an apparatus
for the linear acceleration of electrons that allows to spatially
vary the dose of radiation that is incident to a given tumoral
area.
Another object of the present invention is to provide an apparatus
for the linear acceleration of electrons having a modest size and
weight.
Another object of the present invention is to provide an apparatus
for the linear acceleration of electrons that avoids the need for
the external focusing and centering devices for the emitted
electron beam that are present in prior-art accelerators.
Another object of the present invention is to provide an apparatus
for the linear acceleration of electrons that allows to eliminate
the cathode from the acceleration structure.
Another object of the present invention is to provide an apparatus
for the linear acceleration of electrons that is highly reliable,
relatively easy to manufacture, and at competitive costs.
This aim, these objects, and others which will become apparent
hereinafter are achieved by an apparatus for the linear
acceleration of electrons, particularly for intraoperative
radiation therapy, characterized in that it comprises:
an articulated structure for moving irradiation means that comprise
an acceleration structure constituted by a plurality of
cavities;
modulation means for generating, controlling, and transmitting a
radio-frequency to said cavities of said acceleration structure;
and
processing and control means adapted to control said apparatus,
said modulation means being separate from said irradiation means,
the connection occurring by virtue of waveguide means adapted to
carry the radio-frequency to said acceleration structure.
BRIEF DESCRIPTION OF THE DRAWINGS
Further characteristics and advantages of the invention will become
apparent from a preferred but not exclusive embodiment of the
apparatus according to the invention, illustrated only by way of
non-limitative example in the accompanying drawings, wherein:
FIG. 1 is a view of a known type of apparatus for the linear
acceleration of electrons;
FIG. 2 is a view of the configuration of the acceleration cavities
for a known type of acceleration apparatus;
FIG. 3 is a view of the configuration of the acceleration cavities
for an acceleration apparatus according to the invention;
FIG. 4 is a block diagram of an apparatus for the linear
acceleration of electrons according to the invention;
FIG. 5 is a lateral elevation view of a robot and of the radiating
head connected thereto, said robot and said head being a part of
the acceleration apparatus according to the invention;
FIG. 6 is a flowchart of the steps for the characterization of an
area of the body of a patient to be treated with the apparatus
according to the invention; and
FIG. 7 is a flowchart of the operating steps for scanning
irradiation by using the apparatus according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
With reference to FIG. 1, the known acceleration apparatus
comprises a radio-frequency modulator 1, a magnetron 2, cathode
modulation means 3, circulation means 4, a load of cooling water 5,
an acceleration structure 6, a focusing magnet 7, a centering
magnet 8, a deflector magnet 9, a beam diffuser 10, a beam
equalizer 11, a beam applicator 12, and a beam collimator 13.
FIG. 2 illustrates in detail the acceleration structure 16 of the
acceleration apparatus of FIG. 1, which is constituted by a set of
acceleration cavities 16, by a cathode 18 connected to the first
acceleration cavity, and by a titanium plate 15 aligned with the
axis of the last acceleration cavity.
The acceleration cavities 16 are enclosed by an external
vacuum-tight jacket 14, and two magnets 17 are located outside said
external jacket 14. The function of the two magnets is to induce
the magnetic field strength that is required for the collimation of
the electron beam along the axis of the acceleration structure.
With reference instead to FIGS. 3, 4, and 5, the acceleration
apparatus according to the invention comprises control and
processing means 30.
The control and processing means 30 comprise: power supply means
31; processing means 40, which advantageously comprise a computer;
the cooling system of the apparatus; the means for distributing
motive power; and the safety devices (not shown).
The control and processing means 30 are connected to modulation
means 33 that comprise radio-frequency modulation means 34
connected to a magnetron 35 and to cathode modulation means 36. The
magnetron 35 is protected from accidental load reflections by a
ferrite isolating system 37.
Waveguide means 38, conveniently constituted by a flexible
waveguide, connect the radiofrequency modulation means 33 to
irradiation means, constituted by a radiating head 32 that
comprises an acceleration structure 39 constituted by a plurality
of acceleration cavities 26 (also known as resonant cavities)
arranged in series one next to the other. The acceleration cavities
are connected to each other by vacuum-tight braze welding.
The acceleration cavities 26 of the acceleration structure 39 are
designed so as to produce radio-frequency self-focusing along the
X-axis of said cavities. Self-focusing has been obtained by using
different length values for the first, second, third, fourth and
fifth acceleration cavities, so that the lengths increase from the
first cavity to the fifth one and are constant for the subsequent
cavities. Particularly, it has been found that the optimum lengths
for the first, second, third, fourth and fifth cavities are 25 mm,
40 mm, 45 mm, 48 mm and 50 mm, respectively. The energy of the
electrons and their capture have also been treated for the first
cavity, in which the electrons are not yet relativistic and the
values of b and r (Lorenz parameters) vary appreciably.
For an in-depth treatment of radio-frequency self-focusing of
electrons, reference should be made to J. Livingood, "Principles of
particle accelerators", Argonne National Laboratory, Van Nostrand
Company, N.Y., 1961.
A cathode 28 is placed in front of the first acceleration cavity
and is supplied by the cathode modulation means 36; a thin titanium
lamina is arranged outside the last acceleration cavity for vacuum
tightness.
In FIG. 4, the reference numeral 41 designates a particular area of
the body of a patient that must be treated by irradiation by means
of the apparatus according to the invention.
FIG. 5 is a lateral elevation view of the apparatus according to
the invention, in which the reference numeral 50 designates a
supporting structure fixed to the floor or resting thereon.
An articulated structure 51 is located on the supporting structure
50 and is meant to support and move the radiating head 32; a
diaphragm 60 is applied to said radiating head in the position
where the electronic beam exits.
In detail, the articulated structure 51, commonly termed tube
support, is constituted by a vertically arranged robot comprising
four articulated and mutually interconnected segments designated by
the reference numerals 51a, 51b, 51c, and 51d, which allow to
arrange the radiating head 32 in any spatial position.
The articulated segments 51a, 51b, 51c, and 51d are mutually
pivoted so as to give the radiating head 32 six degrees of freedom
in space.
In particular, the articulated segment 51a is rotatable about the
rotation axis 52 of the supporting structure 50 both clockwise and
counterclockwise; the articulated segment 51b is rotatable in both
directions about the hinge axis 53; the segment 51c is rotatable in
both directions about the hinge axis 54 as well as about the axis
56; and the segment 51d is rotatable in both directions about the
hinge axis 55.
The reference numeral 57 designates a supporting post for an
operating table 58. Said post rests on a footing 59 that is
moderately shielded, with respect to the floor, only if access to
the rooms beneath the operating room is not prohibited during use
of the apparatus according to the invention. Said shielding is not
necessary otherwise.
Control means, advantageously comprising a movable button panel 61,
control the apparatus according to the invention.
FIGS. 6 and 7 are flowcharts of the operating steps of the
apparatus according to the invention, which are handled by the
processing means 40.
With reference to the above figures, the operation of the apparatus
for the linear acceleration of electrons according to the invention
is as follows.
The robot constituted by the articulated segments 51a, 51b, 51c,
and 51d allows to orientate the radiating head 32 so as to direct
the electron beam exactly onto the region where the therapy is to
be performed. The possibility of orientating the radiating head 32
allows to avoid expanding the beam and therefore allows precise
treatment of the region to be irradiated, bringing the radiating
head 32 very close to the region to be irradiated. This, in
comparison with the minimum possible distance that can be obtained
with known linear accelerators, which varies from 80 to 100 cm,
allows the apparatus according to the invention to have a much
higher efficiency, since there is no beam scattering and a much
lower power level is thus required.
Continuous measurement of the position of the various articulated
segments that constitute the robot occurs by means of a sensor
system (not shown) with which the robot is equipped.
The processing means 40 allow to predefine the desired movements of
the articulated segments 51a14 51d that constitute the robot, and
therefore of the radiating head 32, so that said radiating head
closely follows the contour of the region to be irradiated; it is
furthermore possible to set the desired doses of radiation for each
point of the region to be treated.
The modulation means generate and control the radio-frequency and
feed to the cathode 28. The generated radio-frequency is sent to
the acceleration cavities by means of the flexible waveguide
38.
The electrons that move along the axis of the acceleration cavities
26 are gradually accelerated by the radio-frequency field inside
each cavity 26 until they reach the desired final energy. The
electrons exit from the acceleration structure 32 through the thin
titanium lamina 25, the thickness whereof allows the electrons to
pass therethrough without losing an appreciable part of the energy
they possess.
The radio-frequency electric field used to accelerate the electrons
is produced by the magnetron 35, which feeds the acceleration
structure 32 by means of the waveguide 38.
The modulator of the cathode 36 feeds the cathode and synchronizes
its operation so that the train of radio-frequency pulses that
feeds the acceleration structure 32 is matched by an emission of
electrons on the part of the cathode.
The beam of electrons is focused and accelerated simultaneously in
the first cavities with a set combination of the cathode injection
energy and of the length of the first, second, third, fourth and
fifth cavities, and can pass through the center of the subsequent
cavities of the acceleration structure after the peak of the
radio-frequency, so as to undergo additional focusing.
The beam of electrons is pulsed, and each pulse lasts 4
microseconds. The frequency of the pulses can be fixed or
variable.
Use of self-focusing of the electron beam allows to eliminate
auxiliary devices used in known accelerators, and in this manner
the electron beam does not encounter metallic masses along its path
and therefore does not produce radiation, allowing to use the
apparatus according to the invention directly in the operating room
without particular protective measures.
Use of the processing means 40 allows to use the apparatus
according to the invention for mechanical scanning irradiation. The
operating procedures required for this scanning irradiation
comprise four different operating states of the acceleration
apparatus.
These four states are:
instruction step;
learning step;
verification step; and
therapy step.
FIG. 6 is a block diagram of the sequence of steps for defining an
area to be irradiated, which is called "source plane", performed by
the processing means 40; in said figure, after the initial step
100, there is a step 110 for selecting the plane on which the area
to be irradiated lies; the step 110 is followed by the step 120 for
selecting the inclination angle of the radiating head 32 with
respect to the defined source plane; this is then followed by the
step 130 for entering the vertices of the figure to be irradiated,
the step 140 for tracing the perimeter of the figure for
confirmation, the step 150 for calculating the data for
irradiation, the irradiation step 160, and finally the end step
170.
With reference now to FIG. 7, when the patient is ready for
electron therapy (step 200), the apparatus according to the
invention is placed (step 210), by opening the articulated
structure 51, so that its beam direction indicator is trained on
the center of the area to be treated. This movement is controlled
by means of the movable button panel 61.
At this point, the apparatus is placed in the learning state: the
operator starts to move the beam over a path that coincides with
the edge of the region to be treated; this path is developed over
more or less spaced points, depending on the complexity of the
profile, and the processing means 40 interpolate and connect the
various points with straight segments or circular arcs.
Once the path has been closed (step 220) the operator can start
another one (step 230) if the therapy recommends treatment with
fields that are differentiated in terms of dose and/or energy; the
various fields thus formed can be concentric or separate.
Once learning has ended, the apparatus is placed in the
verification step, during which the operator enters (steps 240 and
260), the required dose and the corresponding energy for each field
and the articulated structure 51 constantly moves (steps 250 and
270) along the corresponding paths with its light beam.
Once the verification step has ended, the steps for the irradiation
of the various fields (steps 280, 290, and 300) occur. These
irradiation steps can be followed on the monitor of the processing
means 40, which displays data related in real time to the path in
progress, the percentage of treatment performed, the dose given,
and the remaining dose.
This is followed by the end step 310.
In the case of conventional irradiation, the operator, after moving
the radiating head 32 close to the patient, and after setting the
desired dose by virtue of the processing means 40, moves the
radiating head 32 towards the collimator cone that is used to
protect the parts of the patient's body that are not to be
irradiated from the electron beam, and begins the irradiation.
In practice it has been observed that the apparatus according to
the invention fully achieves the intended aim, since it allows to
provide an apparatus for the linear acceleration of electrons that
can be used directly in the operating room without particular
protective measures. Furthermore, the apparatus according to the
invention is much smaller, lighter, and cheaper than similar known
apparatuses.
The separation between the radiating head 32 and the modulation
means 33, and their connection by means of the flexible waveguide
38, allow to provide an articulated mechanical arm 51 capable of
positioning and moving in space the acceleration structure 39 and
the radiating head 32 with extreme precision and in a very flexible
manner.
Control by means of an appropriately programmed computer 40 allows
to set up the movement of the articulated structure 51 so that the
beam of electrons treats the entire tumoral mass, no matter how
irregular it might be.
The beam self-focusing characteristic, combined with the shape of
the acceleration structure 32, make it unnecessary to have
auxiliary external devices for regulating the beam (magnets,
etcetera), thus allowing a very low X-ray level. This reduction in
radiation allows to use the apparatus in operating rooms without
particular shielding.
The use of vacuum-tight braze welding to assemble the various
acceleration cavities 26 that constitute the acceleration structure
32 allows to eliminate the external vacuum-tight jacket, thus
reducing weight and size.
The device thus conceived is susceptible of numerous modifications
and variations, all of which are within the scope of the inventive
concept.
Thus, for example, since in the apparatus according to the
invention the cross-section of the beam remains very small, the
current of the beam must in turn be reduced considerably, on
penalty of risking the delivery of an excessive local dose and
therefore necrotizing the irradiated tissue. The need to reduce the
intensity of the current can allow to eliminate the cathode 28 from
the acceleration structure 39 by virtue of the known phenomenon of
cold extraction of electrons from a metallic material. This
phenomenon consists of the fact that an intense electric field
applied to a metallic material is able to extract a certain number
of electrons from the outermost atomic orbits. The number of
electrons that can be extracted, however, is not sufficient for the
beam currents required by known accelerators.
Finally, all the details may be replaced with other technically
equivalent elements.
In practice, the materials employed, so long as they are compatible
with the specific use, as well as the dimensions, may be any
according to the requirements and the state of the art.
* * * * *